1. Field of the Invention
The present invention relates to a semiconductor optical device, and more particularly, to a semiconductor optical device having a structure which prevents damage to a waveguide area which has a ridge structure.
2. Description of the Related Art
FIGS. 5A and 5B show a conventional semiconductor laser generally denoted at 500. FIG. 5A shows a top view of the laser 500 and FIG. 5B shows a cross sectional view of the laser 500 taken along a direction V—V of FIG. 5B.
The semiconductor laser 500 comprises a semiconductor substrate 1 having a front surface and a back surface. A buffer layer 2 is disposed on a surface of the semiconductor substrate 1. The buffer layer 2 has a stripe-shaped structure which protrudes upward in the form of stripes, and an active layer 3 is disposed on the buffer layer 2. A current blocking layer 4 buries both sides to the active layer 3, and a contact layer 5 is disposed on the current blocking layer 4.
Mesa trenches 6 extending to the semiconductor substrate 1 are disposed on both sides to the buffer layer 2 which has the stripe-shaped structure, thereby defining a waveguide area 20 sandwiched by the mesa trenches 6 and mount areas 21 and 22 which are located on both sides of the waveguide area 20.
A protection film 8 is disposed on the contact layer 5 and a surface of the semiconductor substrate 1 which contains the insides of the mesa trenches 6, and a metal plate layer 10 is disposed on the protection film 8. The metal plate layer 10 is connected with the contact layer 5 through an opening 9 which is formed in the protection film 8 within the waveguide area 20. Further, a metal plate layer 12 is disposed to the back surface of the semiconductor substrate 1.
In the semiconductor laser 500, the top edge of the waveguide area 20, namely, the top surface of the metal plate layer 10 is higher than the top edge of the mount area 22, namely, a surface of the protection film 8. Hence, the waveguide area 20 is subjected to a stress at a manufacturing step and/or a mounting step, and fractures or is damaged, thus inviting a problem that the production yield deteriorates. To be more specific, the waveguide area 20 is damaged at a step of vacuum-sucking the semiconductor laser 500 on the front surface of the semiconductor laser 500 and thereby holding the semiconductor laser 500 and mounting the semiconductor laser 500 to a package, at a step of coating edge surfaces with a plurality of semiconductor lasers 500 stacked one atop the other, or at other steps.